1. Field of the Invention
The present invention refers to hermetically sealed lead acid bipolar batteries. More specifically, the invention relates to a method of coupling a plastic frame to the peripheral edge of an electrode plate, so that the latter constitutes a modular peripheral member providing junction to equal adjacent members for hermetically sealing the cells of the battery.
2. Description of Prior Art
Several prior art documents disclose a typical arrangement comprising a frame of plastic insulating material coupled to an electrically conductive polymer plate acting as a substrate for active compounds and dividing the cells.
The frame is applied along the peripheral edge of the generally rectangular plate, defining the working surface of the electrochemical cell.
The frame supports the cell partitioning members and forms a wall delimiting the space between the electrodes and providing sealing and Junction of the single cells with adjacent cells. Also, the frame provides a liquid and air-tight hermetical seal with respect to the exterior.
The following are known methods for coupling a peripheral frame to the electrode plate:
a) forming a frame by injection or pressure molding.
Along the inner side of the frame a peripheral recess is formed for accommodating the outer edge of the electrode plate. The two parts are fixed together by a tongue and slot arrangement, as disclosed in U.S. Pat. No. 4,900,643. As an alternative, the peripheral edge of the plate joined to the walls of the slot by heat welding or ultrasonic welding or adhesives, as described in U.S. Pat. No. 4,164,068.
b) the frame is fixed to the plate surface by mold injection, simultaneously providing positioning and sealing of the frame on the central plate, as discussed in both of the cited references.
The first of the two cited methods, providing a mechanical junction, encounters a problem in that it does not guarantee hermetic seal. In addition, a second drawback derives from the application of adhesives or final heat treatments for welding the edge of the plate to the recesses formed in the body of an outer mounting frame. The final result is not reliable and also involves rather complex operations.
The second method involves deformation problems at the edges of the plates and insufficient adhesion may result when conventional injection molding is carried out, as a consequence of high working pressure and insufficient contact time between the parts to be welded.